Malignant infantile osteoporosis is a fatal congenital disease wherein afflicted individuals are incapable of remodeling their bones. Abnormally thickened and dense bone is formed and any space enclosed normally bone by bone is compressed or obliterated. Calcitriol, the active form of Vitamin D, or steroid hormones sometimes help such infants. Our protocol is designed to see whether these drugs can be used together and whether the combination will work better than either alone.